Process for biodegradatioon of soil contaminants that contain volatile/semivolatile components

ABSTRACT

A biodegradation apparatus comprising an enclosed vessel for holding a large volume of soil contaminated with hydrocarbons. Air diffusers uniformly within the vessel force moistened air through the vessel thereby removing volatile hydrocarbons from the contaminated soil. Outgoing air is supplied to vapor phase bioreactor for the removal of hydrocarbon contaminants from outgoing air. The outgoing air is next supplied to a granular activated carbon filter system which absorbs remaining hydrocarbons and then expels non-polluted air into the atmosphere concluding phase one treatment of the hydrocarbon contaminated soil. Phase two treatment of the hydrocarbon contaminated soil is initiated by utilizing high pressure injection nozzles to force water with surfactant additives through the soil thereby forming at the upper portion of the enclosed vessel a supernatant which includes hydrocarbon contaminants. The supernatant is next provided to a settling tank that collects oily sludge at the bottom thereof and then to a treatment tank where nutrients are added to promote biological growth for biodegradation of the remaining hydrocarbon contaminants.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to biodegrading contaminatedsoils and, in particular, to a method and apparatus for the removal ofvolatile hydrocarbons and the like from contaminated soils.

2. Description of the Prior Art

Recent environmental legislation such as the Comprehensive EnvironmentalResponse, Compensation and Liability Act of 1980 and the SuperfundAmendments and Reauthorization Act of 1986 have identified certainhazardous waste sites as requiring cleanup utilizing treatmenttechnologies that will permanently and significantly reduce the volume,toxicity, or mobility of hazardous substances at these waste sites. Thislegislation further directs that permanent remedies be chosen for thecleanup of these hazardous waste sites and that offsite disposal ofcontaminants should be the least favored alternative for disposal ofhazardous waste.

In complying with this environmental legislation the military hasidentified a significant number of their facilities as being hazardouswaste sites requiring cleanup. Typically, the soils at these sites arecontaminated with highly volatile hydrocarbon compounds such asgasolines and chlorinated solvents as well as hydrocarbon compoundshaving moderate to low volatility such as jet fuel, diesel fuel, engineoil and lubricants.

These hazardous waste sites also have underground storage tanks whichare regulated by this environmental legislation and which are being usedto store diesel fuel, gasoline and jet fuels. A significant portion ofthese underground storage tanks are over twenty years old or arefabricated from concrete which is permeable to most organic liquids.Thus, there is a high probability, with some estimates exceeding fiftypercent, that these underground storage tanks are leaking and thuscontaminating the soils surrounding the underground storage tanks.

Biodegradation has long been recognized as a process for the removal oftoxic chemicals from the environment. In the past, for example,wastewater treatment plants have used biological processes to removetoxic chemicals and other contaminants from wastewater.

Bioremediation, which is the controlled use of biodegradation to removetoxic contaminants from soil, water and the like has also been used toremove petroleum hydrocarbons from contaminated surface soils and water.Bioremediation generally relies on the hydrocarbon degrading abilitiesof biological materials such as bacteria, fungi, bacterial enzymes, orfungal enzymes to degrade hydrocarbon contaminated soil. The hydrocarbondegrading biological materials are often naturally present incontaminated soil and given sufficient time can naturally degrade thehydrocarbon contaminants. In addition, this natural degradation processcan often be promoted by directly adding biological materials such ashydrocarbon degrading microorganisms to soil in an amount sufficient todegrade the hydrocarbon contaminants or by encouraging the proliferationof hydrocarbon degrading organisms either naturally present in soil orpresent as a result of inoculation.

Bioremediation of hydrocarbon contaminated soils is favored over soilremoval or chemical treatment of soil because of lower cost, proveneffectiveness and ability for reduction of hydrocarbon contamination.While satisfactory for their intended purpose of removing contaminantssuch as hydrocarbons from soil, prior art bioremediation processesordinarily leave something to be desired in that even under optimumconditions, months or years may be required to decrease the levels ofhydrocarbon contamination to the desired levels. This disadvantage hasgreatly limited the potential use of bioremediation to reducehydrocarbon contamination in soils.

It is therefore an object of this invention to provide an apparatus andmethod for accelerated biodegradation of hazardous organic substances insoils.

It is a further object of the present invention to significantly reducethe levels of hydrocarbon contamination of soils within a relativelyshort period of time after arrival at the hazardous substancecontaminated site.

It is yet a further object of the present invention to provide a methodand apparatus which permits continual, effective and highly efficienttreatment of hydrocarbon contaminated soils.

Various other objects and advantages of the present invention willbecome more apparent to those skilled in the art as a more detaileddescription of the invention is set forth below.

SUMMARY OF THE INVENTION

The above and other objects of the present invention are accomplished bya biodegradation apparatus comprising an enclosed primary vessel that isimpermeable to liquids and which is capable of holding a large volume ofsoil contaminated with hydrocarbons such as gasoline, oil, chlorinatedsolvents and the like. Air diffusers uniformly positioned at the bottomof the vessel force moistened air through the vessel thereby removingvolatile hydrocarbons from the contaminated soil at an accelerated rate.Outgoing air from the vessel is provided to a vapor phase bioreactor forthe removal of volatilized hydrocarbon contaminants in the outgoing air.The outgoing air is next supplied to a granular activated carbon filtersystem which absorbs remaining hydrocarbons and then expels non-pollutedair into the atmosphere. This extraction of volatile hydrocarbon vaporsfrom the soil constitutes the first phase of the biodegradation processimplemented by the present invention.

Phase two treatment of the hydrocarbon contaminated soils is initiatedby utilizing high pressure injection nozzles to force water withsurfactant additives through the soil thereby forming a fluidized soilsuspension in the lower portion of the enclosed vessel and at the upperportion of the enclosed vessel a supernatant layer which includeshydrocarbon contaminants. The hydrocarbon contaminants in thesupernatant may be an oily film or emulsion, or may be attached to finesuspended clay sized particles The supernatant is next provided to asettling tank that collects oily sludge and particulates at the bottomthereof and then to a treatment tank where commercially availablenutrients are added to promote biological growth whereby the remaininghydrocarbon contaminants can be converted by biodegradation intonontoxic by-products. When the water in the second treatment tank isrendered non-toxic thereby being in an environmentally-safe condition,the water is again reinjected with or without an emulsifying agent intothe enclosed primary vessel for treatment of contaminated soils withinthe vessel.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic drawing of biodegradation apparatus constitutingthe present invention

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, there is shown a biodegradation apparatus,designated generally by the reference numeral 10, which may be used toremove hydrocarbon contaminants such as gasoline, diesel, jet fuel,number six fuel oil, lubricant oil, crude oil, or the like from soils.Biodegradation apparatus 10 comprises an above ground holding vessel ortank 12 which may be fabricated from concrete or other nonporousmaterials sufficient in strength to hold a large volume of contaminatedsoil and water mixture 13. Vessel 12 has a removable top 14 which may befabricated from a light weight, high strength plastic and which allowsfor the placement of contaminated soil 13 within vessel 12. Uponplacement of the contaminated soil 13 within vessel 12, removable top 14is sealed by conventional means such as a sealing tape such is airtight, thus being capable of supporting a low negative internalatmospheric pressure.

There is positioned at the bottom portion of vessel 12 a plurality ofevenly spaced air diffusers 16 which forces moistened or dry air throughthe contaminated soil 13. The spacing of the air diffusers 16 withinvessel 12, in turn, provides for a uniform distribution of air flowthrough the contaminated soil 13. A pump 18 draws air from theatmosphere via a pipe 20 through a heater 22 which heats the air to atemperature of 70° F.-90° F., if required, to a manually operateddiverter valve 24. When the contaminated soil 13 in vessel 12 issaturated with water, diverter valve 24 is used to bypass a humidifier26 by diverting air through a bypass pipe 28 to air diffusers 16. Theheated air is then forced through the contaminated soil 13 at a pressureof approximately 30 psi by pump 18 drying the soil and removing from thesoil volatile hydrocarbon vapors. It should be noted that a check valve32 is positioned between the outlet port of humidifier 26 and thejunction of pipe 20 and bypass pipe 28. Check valve 32, in turn,maintains the direction of flow of dry air from heater 22 through bypasspipe 28 to air diffusers 16.

When the contaminated soil 13 within vessel 12 is dry, that is moisturewithin the soil is less then 5%-6% by weight, diverter valve 24 may beset so that pump 18 draws air from the atmosphere through humidifier 26,which moistens the air to air diffuser 16. Pump 18 then forces themoisten air through the contaminated soil 13 removing hydrocarbon vaporsfrom the soil. Apparatus 10 includes conventional moisture tensionlysimeter 34 which measures the moisture content of soil within vessel12 so that an operator or automated system, not shown, can monitor andcontrol the moisture content of soil 13 to insure that moisture contentof the soil remains at 5%-6% by weight. This, in turn, provides foroptimum desorption of hydrocarbon contaminants from the soil withinvessel 12 as well as promoting the biodegradation of the soil withinvessel 12.

There is positioned at the top portion of vessel 12 a plurality ofevenly spaced air intakes 36 which are connected to a pump 38 by a pipe40. Pump 38, which has an operating pressure of approximately 309 psi,withdraws air including hydrocarbon vapors released from contaminatedsoil 13 within vessel 12 through a plurality evenly spaced air intakes36 and pipe 40 to a treatment tank or vessel 42. Tank 42 uses potassiumhydroxide (KOH) or similar compound as an absorbing agent to removecarbon dioxide from the hydrocarbon vapors. Since potassium hydroxide isused to absorb carbon dioxide from the hydrocarbon vapors, it isrequired that there be a periodic removal and replacement of the carbondioxide absorbing agent within tank 42.

At this time it should be noted that biodegradation apparatus 10 mayeffectively treat the outgoing air from vessel 12 to render itenvironmentally safe without tank 42. It should also be noted that thereis operatively connected to pipe 40 a vapor phase detector 44 which may,for example, be a photoionization detector for measuring theconcentration of hydrocarbon vapor within the outgoing air from vessel12.

Pump 38 next forces the hydrocarbon vapors through a pipe 46 to a vaporphase bioreactor 48 for the removal of volatile hydrocarbon contaminantsor other organic vapors. The vapor phase reactor 48 may be a biofilterof granular activated carbon or granular coke, plastic or glass beads,peat or the like. In addition, the bioreactor 48 used in the preferredembodiment of the present invention may be any well known, commerciallyavailable biofilter which is highly efficient, i.e. provides forcomplete removal of hydrocarbon pollutants and odorous substances fromthe outgoing air as well as being simple in construction and operationand providing for low energy consumption (operating cost).

The outgoing air is next supplied through a pipe 50 to a conventionalgranular activated carbon filter 52 which absorbs any remaininghydrocarbon contaminants and then expels non-polluted air through an airexhaust pipe 54 into the atmosphere.

An operator monitoring vapor phase detector 44 will energize a pump 56,which may be any commercially available sludge pump for transportingsludge as well as water, whenever the hydrocarbon vapors flowing throughpipe 40 level off to a predetermined constant value. Pump 56 willinitially draw water from a reservoir, not shown, through a pipe 58, atreatment tank 60, a pipe 62 and a heater 63 to a plurality of evenlyspaced high pressure injection nozzles/water jets 64 positioned at thebottom portion of vessel 12.

Treatment tank 60 has therein conventional and well known surfactantssuch as detergents to penetrate and help loosen nonvolatile hydrocarboncontaminants from soil particles within vessel 12. Injection nozzles 64force water at pressures exceeding 120 psi in an upward direction withinvessel 12 causing the contaminated soil 13 to churn within vessel 12with fine particles of contaminated soil, oil and the like moving in anupward direction thereby forming a supernatant, designated generally bythe reference numeral 65, at the upper portion of vessel 12. The largerparticles of soil, in turn, sink to the lower portion of vessel 12.

At this time it should be noted that gravel may be placed at the bottomof vessel 12 to provide structural support for water jets 64 and airdiffusers 16 at the bottom of vessel 12. In addition, it should be notedthat heater 63 maintains water temperature at approximately 25°-35° C.prior to injection or reinjection of the water into the contaminatedsoil within vessel 12 to accelerate biodegradation and soil washing.Further, there is positioned at the end of pipe 62 a valve 67 which whenopened allows water jets 64 and pipe 62 to be flushed of soils whichwould plug up the water jets 64 and pipes 62.

The supernatant 65 at the upper portion of vessel 12 then exits throughan exit pipe 66 to a settling tank 68, which allows oil sludge and heavynonvolatile hydrocarbon contaminants to accumulate at the bottom portionof tank 68. A pump 72 withdraws water and the remaining hydrocarboncontaminants from settling tank 68 through a connecting pipe 70 to atreatment tank 73. Treatment tank 73 has therein well known,commercially available nutrients to promote biological growth wherebythe remaining hydrocarbon contaminants can be converted intoenvironmentally-safe and non-toxic by-products. The nutrients intreatment tank 73 may be, for example, ammonium nitrate or solublephosphates. In addition, pH buffers such as sodium hydroxide orhydrochloric acid are utilized in treatment tank to maintain a nearneutral pH within treatment tank 73.

When the water within tank 73 is environmentally safe, that is all thehydrocarbon contaminants within tank 73 have been neutralized, anormally closed valve 76 is opened allowing water to be withdrawn fromtank 73 through connecting pipe 74 to tank 60. The environmentally safewater from tank 73 may be recirculated through vessel 12 removingadditional hydrocarbon contaminants from soil 13 until the soil withinvessel 12 is rendered environmentally safe.

Removable top 14 may then be removed from vessel 12 allowing theenvironmentally safe soil within vessel 13 to be removed therefrom andreplaced with hydrocarbon contaminated soil which may then renderedenvironmentally safe by utilizing biodegradation apparatus 10 of thepresent invention.

Biodegradation apparatus 10 includes a pipe 78 having therein a normallyclosed valve 80 which when opened allows oily sludge to be backflushedby pump 56 from the bottom portion of tank 68 to vessel 12 for treatmentby biodegradation apparatus 10 This sludge may contain sufficientquantities of microorganisms to help promote biodegradation of new soilsplaced within vessel 12 for treatment. It should be noted that there ispositioned at the outlet port of heater 63 a check valve 94 whichprevents sludge from flowing back through heater 63.

Biodegradation apparatus 10 also includes a drain pipe 90 which includesa normally closed valve 92 which when opened allows water to be drainedfrom vessel 12 into the surrounding soil. Valve 92, in turn, is utilizedonly when the water within vessel 12 is rendered environmentally safe.

Biodegradation apparatus 10 also includes a drain pipe 98 which includesa normally closed valve 98 which when opened allows water to be drainedfrom tank 60 into the surrounding soil. Valve 96, in turn, is utilizedonly when the water within tank 60 is rendered environmentally safe.

At this time it should be noted that while only biodegradation ofhydrocarbon contaminants by utilizing the apparatus of the presentinvention is described, biodegradation apparatus 10 may be used toremove any biodegradable volatile organic compounds to render soilsenvironmentally safe.

From the foregoing, it may readily be seen that the subject inventioncomprises a new, unique and exceeding useful method and apparatus forthe biodegradation of volatile organic compounds such as hydrocarboncontaminants within soils which constitutes a considerable improvementover the known prior art. Obviously, many modifications and variationsof the present invention are possible in light of the above teachings.It is therefore to be understood that within the scope of the appendedclaims the invention may be practiced otherwise than as specificallydescribed.

What is claimed is:
 1. An apparatus for the continuous treatment ofsoils contaminated with volatile and nonvolatile hydrocarboncontaminants, said apparatus biodegrading said volatile and nonvolatilehydrocarbon contaminants thereby rendering said soils environmentallysafe, said apparatus comprising:an enclosed primary vessel having aremovable top and a bottom, said enclosed primary vessel being adaptedto receive and hold said contaminated soils so as to allow saidhydrocarbon contaminants to be removed from the soils within saidenclosed vessel; a plurality of evenly spaced air diffusers positionedat the bottom of said enclosed vessel; first pumping means for providingmoist air to said enclosed vessel and for forcing said moist air throughsaid air diffusers in an upward direction through said enclosed vesselso as to remove said volatile hydrocarbon contaminants from said soils;a plurality of evenly spaced air intakes positioned at the top of saidenclosed vessel; second pumping means for withdrawing said moist airincluding said volatile hydrocarbon contaminants from said enclosedvessel through said air intakes; a vapor phase bioreactor connected tosaid second pumping means for removing said volatile hydrocarboncontaminants from said moist air withdrawn from said enclosed vessel; agranular activated carbon filter connected to said vapor phasebioreactor for absorbing any remaining hydrocarbon contaminants fromsaid moist air withdrawn from said enclosed vessel; said granularactivated carbon filter having an air exhaust pipe, said granularactivated carbon filter expelling environmentally safe non-polluted airthrough said air exhaust pipe; a plurality of evenly spaced water jetspositioned at the bottom of said enclosed vessel; third pumping meansconnected to said enclosed vessel for providing water to said enclosedvessel and for forcing water provided to said enclosed vessel throughsaid water jets in an upward direction through said enclosed vessel soas to remove said nonvolatile hydrocarbon contaminants from said soils;first treatment tank means connected to said third pumping means forstoring water to be provided to said enclosed vessel, said firsttreatment tank means having therein surfactants, said surfactants beingadded to the water stored within said first treatment tank means toallow the water provided to said enclosed vessel to penetrate and loosensaid nonvolatile hydrocarbon contaminants from said soils, the waterhaving said nonvolatile hydrocarbon contaminants added thereto forming asupernatant, said supernatant being formed within said vessel above saidcontaminanted soils and below said evenly spaced air intakes, saidsupernatant including oil sludge; second treatment tank means connectedto said enclosed vessel; fourth pumping means connected to said secondtreatment tank means for withdrawing said supernatant from said enclosedvessel and providing said supernatant to said second treatment tankmeans, said oil sludge and heavy nonvolatile hydrocarbon contaminantswithin said supernatant settling to the bottom of said second treatmenttank means; third treatment tank means connected to said fourth pumpingmeans, said third treatment tank means having nutrients to effectbiological growth of microorganisms within said nonvolatile hydrocarboncontaminants such that the remainder of said nonvolatile hydrocarboncontaminants are degraded and converted into a non-toxic condition; saidthird treatment tank means being connected to said first treatment tankmeans so as to return water treated within said second and thirdtreatment tank means to said first treatment tank means.
 2. Thebiodegrading apparatus of claim 1 further comprising fourth treatmenttank means connected to the said second pumping means and said vaporphase bioreactor for removing carbon dioxide from said moist airwithdrawn from said enclosed vessel.
 3. The biodegrading apparatus ofclaim 1 wherein said vapor phase bioreactor comprises a biofilter ofactivated granular carbon.
 4. The biodegrading apparatus of claim 1wherein said vapor phase bioreactor comprises a biofilter of granularcoke.
 5. The biodegrading apparatus of claim 1 wherein said vapor phasebioreactor comprises a biofilter of glass beads.
 6. The biodegradingapparatus of claim 1 wherein said vapor phase bioreactor comprises abiofilter of peat.
 7. The biodegrading apparatus of claim 1 furthercomprising a vapor phase detector effectively connected to said enclosedvessel for measuring the concentration of hydrocarbon vapor within theair being withdrawn from said enclosed vessel.
 8. The biodegradingapparatus of claim 1 further comprising a moisture tension lysimeteroperatively connected to said enclosed vessel for measuring the moisturecontent of said soils within said enclosed vessel.
 9. The biodegradingapparatus of claim 1 further comprising a normally closed valveconnected between said first and third treatment tank means.
 10. Thebiodegrading apparatus of claim 1 further comprising a return pipeconnected between the bottom of said second treatment tank means andsaid third pumping means, said return pipe having therein a normallyclosed valve which when opened allows oil sludge to be backflushed bysaid third pumping means from the bottom of said second treatment tankmeans to said enclosed vessel.
 11. The biodegrading apparatus of claim 1further comprising a heater connected between said first treatment tankmeans and said third pumping means and a check valve connected betweensaid heater and said third pumping means.
 12. The biodegrading apparatusof claim 1 wherein said enclosed vessel is fabricated from a nonporousmaterial.
 13. The biodegrading apparatus of claim 12 wherein saidnonporous material is concrete.
 14. The biodegrading apparatus of claim1 wherein said first pumping means comprises:a pump having an inlet portand an outlet port, the outlet port of said pump being connected to saidair diffusers within said enclosed vessel; a humidifier having an inletport and an outlet port; a diverter valve having an inlet port and firstand second outlet ports, the first outlet port of said diverter valvebeing connected to the inlet port of said humidifier; a check valvebeing an inlet port connected to the outlet port of said humidifier andan outlet port connected to the inlet port of said pump; and a bypasspipe connected between the second outlet port of said diverter valve andthe inlet port of said pump.
 15. The biodegrading apparatus of claim 14further comprising a heater having an inlet port adapted to receive airand an outlet port connected to the inlet port of said diverter valve.